1. Field of the Invention
The present invention relates generally to an apparatus for injecting drugs into a person and, more specifically, to an autoinjection device that utilizes a piston-like assembly and a propellant to automatically inject a single dose of a drug into a person when the propellant is activated.
2. Background of the Invention
Presently available autoinjection systems are relatively large and bulky, requiring skill and training in order to properly operate the device and thus are not amenable to applications for which rapid administration of either a single drug or a combination of different compounds in rapid succession is desirable. Such systems are used mainly for mass vaccinations, self-administration of medications, such as for injection of insulin in diabetic patients, epinephrine in anaphylactic shock, or antimigrain drugs (e.g., sumatriptan). Automated injectors used for mass vaccinations, like in military applications, are typically bulky devices that use the same injection head for all patients and often require an external supply of compressed gas.
Autoinjectors are also presently in use for parenteral administration of medications under field conditions, where injections with a syringe are either impractical or require excessive attention or training. Examples of such situations are administration of chemical warfare antidotes (e.g., atropine) and treatment of anaphylactic shock (e.g., epinephrine). In both instances, drug administration must be rapid, simple and reliable and must minimize the possibility of human error on selection and administration of drug doses. One such autoinjector used by the military comprises an elongate tube with a needle protruding from one end. The needle is rapidly and forcefully inserted into a muscle resulting in the injection of a drug contained within the tube. Upon removal of the needle, however, the needle remains exposed and thus requires proper handling to prevent contact by and injury to other persons.
For mass vaccination programs, reduction of the delivery costs associated with immunizations presents the biggest opportunity to boost immunization coverage rates. One way to decrease costs is to reduce the number of contacts required to complete the immunization series. Frequently, patients' compliance is a major factor limiting effectiveness of mass vaccination programs--children, parents, and health care providers are less willing to accept the increased numbers of separate injections. Thus, it is desirable to deliver as many vaccines as possible during a single, quick patient visit. Mixing of vaccines in one syringe is contraindicated due to reduced potency of the mixed vaccines. However, vaccines are typically safe and effective when administered at the same time at different application sites, such as through a single, multiple-site injection. Therefore, there is a clear need to simultaneously inject several vaccines. Due to problems associated with typical needle injections including transmission of disease between patients, hazards to health-care workers, and expensive handling and disposal procedures, a method of injection without the use of a needle or with a retractable needle is desirable.
U.S. Pat. No. 5,167,625 to Jacobsen et al. discloses an implantable drug delivery system which includes a housing having a plurality of compartments each of which includes a flexible drug containment sack. A cover is disposed over the compartment openings to prevent the release of drug formulation contained in the sacks. Gas generating elements are disposed in the compartments and are responsive to an initiation signal for producing gas to force the sacks and drug formulations out of the housing.
A portable, hand-held injection device is disclosed in U.S. Pat. No. 5,616,132 to Newman and includes a diaphragm mounted within a housing having a needle associated therewith that moves in response to movement of the diaphragm when pressurized gas is released into the housing. Each device, however, is a completely self contained unit that would be relatively expensive to manufacture and difficult, if not impossible, to reuse. Accordingly, such a device would be impractical for mass injection scenarios as previously discussed.
Thus, it would be advantageous to provide a prefilled, interchangeable injection module that is disposable, inexpensive, easy to use, and safe for both the patient and medical personnel. It would also be advantageous to provide a prefilled, interchangeable injection module that reduces risks associated with cross-infection, improves compliance, especially in children, improves the effectiveness of vaccination programs, does not require special sharps handling and has smaller numbers of contaminated items to dispose.